The subject invention is directed toward the valve art and, more particularly, to a poppet-type excess flow valve.
Excess flow valves are typically used in flow systems to shut off the flow of process or system fluid whenever it exceeds a predetermined level. For example, rupture of a downstream line, or other failure of a downstream component, could result in release of large amounts of fluid. Depending on the type of fluid involved, the results could be catastrophic.
A satisfactory valve of the general type under consideration should be entirely automatic in operation and require no form of external activation. Preferably, the valve should be totally passive during proper system functioning and allow normal flow therethrough in the manner of a fixed orifice. The flow rate of the valves at the trip point should be distinctly defined and repeatable. At all flow rates up to the trip point, the valves should be stable with no flutter or chatter. In addition, the valves must, of course, be highly reliable and basically maintenance free. Moreover, they should preferably create a minimal restriction to flow during normal flow conditions.
A valve of this kind normally remains in a static condition, never moves, is never exercised, and, if all goes well, never has to trip. Therefore, in many systems such as petroleum or chemical plants, it could easily become clogged by solids, contaminants, tars, waxes, and other materials such systems typically deposit on piping walls. If the holes in the poppet gradually built up a deposit layer and became smaller, they would eventually make it trip a flow rate less than the original design value and result in false trips and the attendant maintenance costs.
While many different valves are currently in use for excess flow control, almost none can satisfactorily meet all the noted criteria in a simple and effective manner. For example, most common excess flow valves are not inherently stable because they function similarly to a simple check valve. To explain, in these known excess flow valves, the flow passes around a poppet or ball and creates a pressure drop. As the flow increases, the poppet gradually compresses a spring and moves toward a seat. At flow rates between open and close stops, the poppet is supported only by the spring and invariably chatters. The flow rate at which the poppet reaches the closed stop can vary widely and thus does not have a distinct, repeatable value.